In a letter to Agriculture Secretary Tom Vilsack, Pingree says the Agriculture Department should stop buying ground beef that contains pink slime, which she describes as an “industrial slurry of beef scraps and connective tissue.”

Pingree says fast-food restaurants such as McDonald’s and Burger King have stopped using the byproduct, and that school cafeterias should, too.

The USDA is set to announce Thursday that schools will be able to choose whether or not they buy ground beef that contains the ammonia-treated filler.